1. Field of the Disclosure
The present invention relates generally to photodetectors, and more specifically, the present invention is directed to imaging systems including photon counters.
2. Background
A silicon photomultiplier (SiPM) is one type of photodetector that is capable of detecting a low intensity single, as low as a single photon. An SiPM device may use a digital counter to count incident photons until a threshold count of incident photons is reached. SiPMs are semiconductor photosensitive devices made up an array of Geiger-mode photon detection cells such as single photon avalanche diodes (SPADs) that are fabricated in a silicon substrate. Geiger-mode photon detection cells have a p-n junction biased beyond its breakdown voltage such that each electron-hole pair can trigger an avalanche multiplication process that translates to a discrete electric pulse. A single photon or multiple photons will not change the amplitude of the resultant pulse from a photon detection cell, since only a single photon is required to trigger an avalanche multiplication process. The avalanche is quenched, either actively or passively, which resets the photon detection cell so that it can detect further incident photons.
An increase in the bit-count of the digital counter would increase the accuracy and/or the count of incident photons, however, this would also increase the silicon area and power consumption required by the SiPM. A counter that requires a large silicon area may prevent an implementation of the circuit into a measurement device.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.